The first weekly insulin dose had me confused

I have been reading about once-weekly insulin and noticed that the starting dose may not always be the same as later doses.

At first I assumed every injection would follow the same pattern, so I am trying to understand why the first dose might be different. Is it related to helping the medicine reach the right level in the body, or does it depend on the person's previous insulin treatment?

For people who have discussed weekly insulin with their doctor, what explanation helped you understand the first dose compared with the doses that come afterward?